【Ifwearedrivingacarorcrossingastreetwewillstopwhenthetrafficlightsturnred.Whydoweuseredratherthanothercolors?Asweknowscattering(散射)happenswhenlightgoesthroughtheair.Forthesamemediaifthewavele】

　　Ifwearedrivingacarorcrossingastreetwewillstopwhenthetrafficlightsturnred.Whydoweuseredratherthanothercolors?

　　Asweknowscattering(散射)happenswhenlightgoesthroughtheair.Forthesamemediaifthewavelength(波长)islongthescatteringwillbeshort.Ifthewavelengthisshortthenthescatteringwillbelong.

　　Ofalllightwecanseeredhasthelongestwavelengthsothescatteringistheweakest.Thatmeanstheredlighttravelsfar.Infactittravelsfartheronrainydays.

　　Usingtheredlightcanhelpdriversinfartherareasseethelights.Ithelpsdriversslowdownorstopintime.Ifdriversdon’tseetheredlightuntiltheyareclosetheymaynotbeabletostopthecarintime.Anaccidentmayhappen.Redcanalsoexcitepeople.Wecanactmorequicklywhenweseethecolorred.

　　Inawordredlighthelpsdriversstopintimeandhelppreventaccidents.

　　1.______hasthelongestwavelengthofalllightwecansee.

　　A.Red             B.Green         C.Yellow         D.Black

　　2.Redlighttravelsfartheron______days.

　　A.windy           B.sunny         C.rainy        D.cloudy

　　3.Redcanmakepeopleactmorequicklybecause____________.

　　A.redcanmakepeoplehappier            B.thescatteringofredisveryshort

　　C.thescatteringofredisverylong         D.redcanmakepeoplemoreexcited

　　4.Theunderlinedword“prevent”means______inChinese.

　　   A.逃避             B.防止          C.处理        D.检查

　　5.Thepassagemainlytellsus____________.

　　A.whyaccidentshappen                   B.howtheredlighttravels

　　C.whyweuseredtrafficlights              D.howtostopintimeattrafficlights